This invention relates to packaging apparatus, and more particularly to apparatus for packaging a product in a tubular bag having its ends sealed closed.
Specifically, this invention relates to an improvement in packaging apparatus as disclosed in U.S. Pat. No. 2,976,657 to Cloud in which a product to be packaged is placed on a web, and the web is formed into a tube around the product and sealed and severed in front of and behind the product to form a bag. In the above-mentioned Cloud patent, the entubed products pass around a so-called rotary turret or wheel. A plurality of clamping assemblies or die sealing units are held stationary in a rest or hold position at one location on the wheel with the wheel rotating relative to the sealing units when the latter are in their hold position. In timed relation to movement of the portions of the tube between successive products therein, the sealing units are released one at a time from the hold position and are coupled to the wheel for being driven by the wheel. Each sealing unit has a fixed lower jaw and a hinged upper jaw swingable from an open to a closed position as the sealing unit moves from the hold position so as to clamp the tube between the jaws intermediate successive products in the tube. The jaws may be heated so as to heat-seal the tube transversely across the tube. Also, the jaws may carry a severing blade (or a heated wire) for severing the tube within the seal formed by the jaws thereby to form the trailing end seal of a leading bag and the leading end seal of a trailing bag. The jaws securely grip the web as the die moves with the wheel and thus pull the tube and products therein through the apparatus at the speed of the wheel.
In the above-mentioned U.S. Pat. No. 2,976,657, the sealing units are maintained in their sealing position substantially perpendicular to the plane of the wheel by means of rollers riding in grooves spaced from the outer edges of the sides of the wheel and extending circumferentially therearound. However, due to the clearance required for rotation of the rollers in their grooves, the sealing units may cock or cant with respect to the plane of the wheel. This cooking or canting of the sealing units results in bags having oblique end seals, and in some instances, results in the sealing units becoming locked to the wheel.
Other packaging apparatus similar to the above-described apparatus are known which utilize another arrangement for coupling and uncoupling the sealing units to the wheel. This other coupling arrangement comprises a bar extending from side-to-side of the sealing unit movable generally in the direction of rotation of the wheel between an uncoupled position in which it is clear of the periphery of the wheel and a coupled position in which it is wedged between an inclined portion of the sealing unit and the outer edge of the wheel thereby to lock the sealing unit to the wheel for rotation therewith. This arrangement is effective for locking the sealing unit to the wheel to prevent movement of the sealing unit in the direction opposite the rotation of the wheel. However, this locking arrangement does not prevent the sealing unit from moving relative to the wheel in the direction of rotation of the wheel. Upon the release of the sealing unit from the hold position, the sealing unit becomes coupled to the wheel and moves with the wheel over the top of the wheel. As the sealing unit moves down from the top of the wheel and before it is engaged by a sealing unit closing cam, the unit is free to fall forward in the direction of rotation of the wheel at a speed faster than the surface speed of the wheel. In known prior art apparatus, brake pads are provided at the ends of each sealing unit engageable with each side of the wheel for applying a braking force to the sealing unit so as to prevent it from falling forward and downward from the top of the wheel at a speed faster than the rotational speed of the wheel. However, with the brakes at the sides of the sealing unit, unequal braking forces may be applied to the sealing unit which may cause the sealing unit to cant or cock relative to the wheel.